Plasma separator-hydrostatic pressure type

ABSTRACT

A blood collection and separator assembly of the type suitable for centrifuging to separate the plasma from the cellular phase of blood is disclosed. The assembly includes a collection container and a piston disposed therein for sealing off the plasma phase from the cellular phase after centrifuging is terminated. The piston has a specific gravity greater than the plasma but less than the cellular phase. Automatic compressible means is associated with the piston and is responsive to increased hydrostatic pressure caused by centrifugation so that the hydrostatic pressure reduces the diameter of the piston to provide a by-pass passage between the walls of the container and the piston so that the cellular phase can pass downwardly around the piston while the plasma phase passes upwardly therearound while the piston comes to rest at the plasma-cellular interface, and when the hydrostatic force is terminated the compressible means expands to form a liquid tight seal to prevent subsequent mixing of the separated phases.

United States Patent Ayres Primary Examiner-Charles N. Hart Assistant ExaminerRobert G. Mukai Attorney, Agent, or Firm-Kane, Dalsimer, Kane, Sullivan and Kurucz 1 July 29, 1975 [57] ABSTRACT A blood collection and separator assembly of the type suitable for centrifuging to separate the plasma from the cellular phase of blood is disclosed. The assembly includes a collection container and a piston disposed therein for sealing off the plasma phase from the cellular phase after centrifuging is terminated. The piston has a specific gravity greater than the plasma but less than the cellular phase. Automatic compressible means is associated with the piston and is responsive to increased hydrostatic pressure caused by centrifugation so that the hydrostatic pressure reduces the diameter of the piston to provide a by-pass passage between the walls of the container and the piston so that the cellular phase can pass downwardly around the piston while the plasma phase passes upwardly therearound while the piston comes to rest at the plasmacellular interface, and when the hydrostatic force is terminated the compressible means expands to form a liquid tight seal to prevent subsequent mixing of the separated phases.

5 Claims, 7 Drawing Figures PATENTED JUL 2 9 i975 SHEET PLASMA SEPARATOR-HYDROSTATIC PRESSURE TYPE BACKGROUND OF THE INVENTION This invention relates generally to plasma separator assemblies and particularly to a plasma separator having a piston and a compressible means associated therewith which automatically compresses when subjected to increased hydrostatic pressure caused by centrifugal force to provide a passageway between the piston and the interior of the collection container so that the cellular phase can pass downwardly around the piston in the container while the liquid or plasma phase passes upwardly therearound.

DESCRIPTION OF THE PRIOR ART It is known to separate blood into its component parts by centrifugation, for example, the assembly disclosed in U.S. Pat. No. 2,460,641. However, this particular assembly does not employ a means for sealing the separated plasma or serum phase from the cellular phase.

It is also known to provide assemblies for manually separating the plasma or serum phase from the cellular phase, for example, as disclosed in U.S. Pat. Nos. 3,586,064; 3,661,265; 3,355,098; 3,481,477; 3,512,940 and 3,693,804. In all of these devices serum is collected in a blood collection container and means are provided for separating the plasma phase from the cellular phase employing filters, valves, transfer tubes or the like.

It is also known to provide assemblies for the sealed separation of blood in which a piston is actuated by centrifugal force such as disclosed in U.S. Pat. Nos. 3,508,653 and 3,779,383. These devices use either a distortable piston made of a resilient material or valve means associated with the piston to affect a sealed separation after centrifugation.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a plasma separator assembly having a piston and a compressible means which automatically seals off the plasma phase from the cellular phase after centrifuging is terminated. It is another object of the invention to provide a piston having means associated therewith which is compressible to provide a path around the piston to permit the passage of the plasma phase to pass upwardly therearound while permitting the cellular phase to pass downwardly therearound and which will automatically seal the piston in the container when centrifuging is terminated.

It is an object of the invention to provide a plasma separator assembly which is economical to manufacture and can be used in conjunction with standard blood collecting equipment.

My invention generally contemplates the provision of than the cellular phase so that the piston will move to the plasma interface and establish a liquid tight seal in the container after centrifuging is terminated.

DESCRIPTION OF THE DRAWINGS For a better understanding of the invention, reference is bad to the drawings which illustrate the preferred embodiments of the invention herein.

FIG. 1 is a sectional elevational view of the plasma separator assembly illustrating a pointed cannula penetrating the stoppered end of the container through which blood is introduced into the container prior to separation.

FIG. 2 is a sectional elevational view after the cannula has been removed and the blood sample has been collected and separated into its phases during centrifugation and the centrifugal force has increased the hydrostatic pressure of the blood and has compressed the automatic compressible means associated with the piston thereby opening a passageway connecting the chamber regions above and below the piston.

FIG. 3 is a view similar to FIG. 2 after the assembly has been centrifuged and the centrifugation has been stopped, the automatic compressible means having been released so as to be in sealing engagement with the container walls.

FIG. 4 is a sectional elevational view of another form of the invention illustrating automatic compressible means mounted on the container wall and in a compressed condition, which provides for the passage of plasma upwardly in the container while the cellular or heavy phase passes downwardly to form an interface between the phases in the container during centrifuging of the assembly.

FIG. 5 is a view similar to FIG. 3 after centrifuging has ceased which illustrates the automatic compressible means in sealing engagement with the piston to form a liquid tight seal which separates the plasma phase from the cellular phase in the assembly.

FIG. 6 is a sectional elevational view of the piston after centrifuging has ceased illustrating another form of the automatic compressible means which can be used in conjunction with the embodiment of FIG. 1.

FIG. 7 is an elevational sectional view of the piston of FIG. 6 when subjected to increased hydrostatic pressure generated by centrifuging the blood filled separator assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the invention here is a description and the drawings of illustrative embodiments, particularly as shown in FIGS. 1-3.

In FIG. 1 the separator assembly 10 comprises a tubular container 12 which is sealed at its open end by closure 14. Closure 14 is preferably made of rubber which is capable of being penetrated by cannula 15 so that blood can be transferred from a blood source into container 12 under aseptic conditions. The closure is made of elastomeric material and should be self-sealing so that when the cannula is removed there will be no loss of blood passing through the penetration portion of closure 14 as illustrated in FIG. 1.

Disposed in container 12 is piston 16 which is preferably made of one or more materials having an average specific gravity of approximately 1.06; for example, polystyrene may be used. Also, piston 16 should be made of a material which is inert to blood and to the resilient O-ring which is mounted in the annular groove 19 of piston 16. The parts forming the assembly may contain an anti-coagulant material. Piston 16 has mounted thereon compressible means such as O-ring 18 which automatically compresses when the assembly is subjected to increased hydrostatic pressure generated by centrifugal force. Compressible means is in the form of an O-ring 18 made of closed cell sponge rubber with a smooth outside surface (or equivalent) normally having an interference fit sealing the piston 16 relative to the container 12. However, when increased hydrostatic pressure is generated by centrifugation, O-ring 18 is compressed unsealing the piston and thereby providing a passageway through which plasma and red cells may flow to form an interface. The piston has a specific gravity of approximately 1.06, which is less than the specific gravity of the cellular phase of blood but is heavier than the plasma phase of the blood. When blood is collected in container 12, as illustrated in FIG. 1, and the container is centrifuged, as illustrated in FIG. 2, the cellular phase will pass downwardly into the bottom portion of container 12 while piston 16 moves upwardly to finally come to rest at the plasma-cellular interface. When centrifuging is terminated the hydrostatic pressure drops and the O-ring l8 expands to form a liquid tight seal, as illustrated in FIG. 3.

FIG. 2 shows conditions during centrifuging. O-ring 18 is illustrated in a compressed condition with piston 16 positioned at the plasma-cellular interface. Compression of O-ring 18 has created passageway 20 between the piston and the inside wall of the container so that the plasma can move upwardly through passage 20 and around piston 16 and red cells can move downwardly through passage 20. When centrifuging ceases, O-ring 18 will expand and re-establish the seal as illustrated in FIG. 3.

Thus, the invention embodiment shown in FIGS. 1-3 includes sealing means responsive to or activated by changes in hydrostatic pressure.

FIGS. 4 and 5 illustrate another form of compressible sealing means responsive to hydrostatic pressure which will automatically form a liquid tight seal to separate the plasma phase from the cellular phase when centrifuging of the assembly is terminated.

FIG. 4 is similar to the embodiment illustrated in FIG. 2 in that assembly is in the process of being centrifuged and compressible means 17' is in a compressed condition to provide passage around piston 16' to permit piston 16 to move upwardly within the container along with the plasma phase while the cellular phase moves downwardly toward the bottom of the container. Container 12' is fitted with a closure 14' of the type described in the embodiment of FIG. 1. Piston 16 is made of material preferably having an average specific gravity of about 1.06 (for example, polystyrene) which is lighter than the cellular phase of blood but heavier than the plasma phase. Compressible means 17 automatically compresses in response to increased hydrostatic pressure generated by centrifugal force, and automatically expands when the centrifugal force is terminated. The compressible means is mounted in the form of a sleeve 17' on the interior surface of the container 12' at a point between the plasmacellular interface so that when piston 16' is permitted to move upwardly in the container piston 16 will come to rest at the plasma cellular interface. Then, when cen- ,4 trifuging is stopped, the piston 16' will be in sealing liquidtight engagement with the compressible means as illustrated in FIG. 5. Compressible sleeve 17' is preferably made of closed cell sponge rubber with a smooth outer skin (or equivalent) and is mounted on the inside surface of container 12.

FIGS. 6 and 7 illustrate another form of compressible sealing means responsive to and actuated by changes in hydrostatic pressure. Piston 16 is formed of a suitable material having an average specific gravity greater than blood plasma but less than that of the cellular phase of blood.

Compressible means 17" is in the form of a substantially non-porous elastomeric sleeve 18" expanded by slightly compressed air (or other suitable gas) and is secured on piston 16" around the upper and lower edges 22, 24 of sleeve 18". Piston 16" is formed having a body portion 25. A plurality of spaced annular grooves 26 are formed in body portion 25. Upper and lower flanges 29 and 27 of body portion 25 form shoulders 29 for mounting sleeve 18" thereon illustrated in FIG. 6. In FIG. 7 compressible means 17" is illustrated in a compressed condition with much of the air compressed into annular grooves 26 due to the increased hydrostatic generated by the centrifugal force so that resilient, compressible element 18" is in a compressed position to form passage 20 to permit the piston to move toward the plasma-cellular interface in a manner comparable to that illustrated in FIG. 2.

In the embodiment of FIGS. 4 and 5 the compressible element 17 is preferably made of a closed cell sponge rubber with a smooth outer skin and is cemented or otherwise fixed to the inside wall of container 12 as illustrated in FIGS. 4 and 5. It should be understood that the piston in the embodiments illustrated herein can be inserted into the assembly prior to use as described or it can be inserted after the blood has been collected by simply removing closure 14 and manually inserting the appropriate piston in the corresponding type container and then centrifuging the assembly to permit the piston to move downwardly in the container to the plasma cellular phase interface rather than upwardly as described. Also, if the pistons are not put into the containers until after the blood has been centrifuged into the light phase and the heavy phase, then these devices can be used for serum, as distinguished from plasma. Then the containers would be centrifuged a second time to move the pistons to the serum red cell interface.

It is also apparent that tube 12 can be formed having openings at each end with the piston positioned at one end so that with blood being collected through the closure member at the opposite end the piston will move downwardly in the container rather than upwardly.

When operating the separator assembly as set forth in the preferred embodiments the blood collection tube 12 which is fitted with closure 14 is preferably evacuated so that when cannula l5 penetrates the closure 14 blood will fill container 12 automatically. It is also contemplated that the separator assembly of the invention herein may be constructed so as to be suitable for use with blood collecting assemblies described in US. Pat. Nos. 3,460,641; 3,469,572 and 3,494,352. It should be understood that when the blood is being collected where the piston 16, 16' or 16" is in the bottom of the container then the blood being collected will be anticoag'ulated so that a clot will not form which might cause a malfunction of the piston.

After the blood has been collected in container 12, assembly is ready for centrifuging. The compressible means, such as the O-ring 18 or the compressible sleeve 17' or the inflated annular ring 18" will be compressed when subjected to increased hydrostatic pressure resulting from centrifugal force. Centrifugation will also cause the serum to pass upwardly in the container around the piston 16 through passage 20 and at the same time for the cellular phase to move toward the bottom of the container while the piston moves towards the cellular-plasma interface. When the blood has been separated the piston will lie at the plasma-cellular interface and when centrifuging ceases the compressible means 18 will re-expand to form a liquid tight seal as shown in FIG. 3. Thus, an assembly is provided in which blood can be controlled, centrifuged, separated into its plasma and cellular phases and shipped through the mails for further analytical determinations without the plasma mixing with the cellular phase even though the assembly is inverted and handled roughly.

While variations of the invention herein may be had, the objectives of the invention have been illustrated and described, it is contemplated that changes in design can be made without departing from the spirit of the invention described herein.

What is claimed is:

1. A piston adapted for use for separating the light phase of blood from the cellular or heavy phase of anticoagulant treated blood disposed in a separator assembly including a blood collection container comprising:

a piston having an average specific gravity heavier than the light phase of blood but lighter than the heavy phase so that when the blood is separated into its component phases the piston will migrate to the light phase-heavy phase interface; said piston comprising;

a body portion which is generally cylindrical and has a diameter less than the internal diameter of the blood collection container; a substantially nonporous, flexible sleeve member mounted around said body portion and sealed around the top and bottom ends thereof, thereby forming an annular space therebetween, said space having a gas therein, said gas having a pressure greater than atmospheric pressure and selected so as to expand the flexible barrier means to form a liquid-tight seal when mounted within the container and said gas being compressible when subjected to increased hydrostatic force so that the flexible barrier means will move away from the inner walls of the container to break the seal and pennit the piston to move toward the cellular-plasma interface when centrifuged.

2. The piston of claim 1 wherein the piston is formed of polystyrene having a specific gravity of substantially 1.06.

3. A blood separator assembly capable of separating anti-coagulant treated blood into its component parts of light phase and heavy phase comprising:

a container having at least one open end which is adapted to receive blood for subsequent separation into a light phase and a heavy phase;

a closure sealing the open end of the container, the closure being formed of a self-sealing, elastomeric material which is penetrable by a cannula through which blood to be separated is conducted into the container;

a piston having an average specific gravity lighter than the heavy phase but heavier than the light phase;

said piston having a body portion which is generally cylindrical and has a diameter less than the internal diameter of the blood collection container;

a compressible sleeve mounted on the interior walls of the container, so as to form a seal with said piston when said piston is positioned within said sleeve and said sleeve is uncompressed, the sleeve being made of closed cell elastomeric material having a smooth surface and said sleeve is responsive to hydrostatic forces whereby when said sleeve is compressed by subjugation to hydrostatic forces, said piston no longer forms a seal with said sleeve, thereby providing a passage for the light phase and heavy phase of the blood to move past the piston.

4. The assembly of claim 3 wherein the piston is formed of polystyrene having a specific gravity of substantially 1.06.

5. The assembly of claim 3 wherein said compressible sleeve is made of closed-cell elastomeric sponge material having a smooth surface. 

1. A PISTON ADAPTED FOR USE FOR SEPARATING THE LIGHT PHASE OF BLOOD FROM THE CELLULAR OR HEAVY PHASE OF ANTI-COAGULANT TREATED BLOOD DISPOSED IN A SEPARATOR ASSEMBLY INCLUDING A BLOOD COLLECTION CONTAINER COMPRISING: A PISTON HAVING AN AVERAGE SPECIFIC GRAVITY HEAVIER THAN THE LIGHT PHASE OF BLOOD BUT LIGHTER THAN THE HEAVY PHASE SO THAT WHEN THE BLOOD IS SEPARATED INTO ITS COMPONENT PHASES THE PISTON WILL MIGRATE TO THE LIGHT PHASE-HEAVY PHASE INTERFACE SAID PISTON COMPRISING, A BODYPORTION WHICH IS GENERALLY CYLINDRICAL AND HAS A DIAMETER LESS THAN THE INTERNAL DIAMETER OF THE BLOOD COLLECTION CONTAINER A SUBSTANTIALLY NON-POROUS FLEXIBLE SLEEVE MEMBER MOUNTED AROUND SAID BODY PORTION AND SEALED AROUND THE TOP AND BOTTOM ENDS THEREOF THEREBY FORMING AN ANNULAR SPACE THEREBETWEEN SAID SPACE HAVING A GAS THEREIN SAID GAS HAVING A PRESSURE GREATER THAN ATMOSPHERIC PRESSURE AND SELECTED SO AS TO EXPAND THE FLEXIBLE BARRIER MEANS TO FORM A LIQUID-TIGHT SEAL WHEN MOUNTED WITHIN THE CONTAINER ANDD SAID GAS BEING COMPRESSIBLE WHEN SUBJECTING TO INCREASED HYDROSTATIC FORCE SO THAT THE FLEXIBLE BARRIER MEANS WILL MOVE AWAY FROM THE INNER WALLS OF THE CONTAINER TO BREAK THE SEAL AND PERMIT
 2. The piston of claim 1 wherein the piston is formed of polystyrene having a specific gravity of substantially 1.06.
 3. A blood separator assembly capable of separating anti-coagulant treated blood into its component parts of light phase and heavy phase comprising: a container having at least one open end which is adapted to receive blood for subsequent separation into a light phase and a heavy phase; a closure sealing the open end of the container, the closure being formed of a self-sealing, elastomeric material which is penetrable by a cannula through which blood to be separated is conducted into the container; a piston having an average specific gravity lighter than the heavy phase but heavier than the light phase; said piston having a body portion which is generally cylindrical and has a diameter less than the internal diameter of the blood collection container; a compressible sleeve mounted on the interior walls of the container, so as to form a seal with said piston when said piston is positioned within said sleeve and said sleeve is uncompressed, the sleeve being made of closed cell elastomeric material having a smooth surface and said sleeve is responsive to hydrostatic forces whereby when said sleeve is compressed by subjugation to hydrostatic forces, said piston no longer forms a seal with said sleeve, thereby providing a passage for the light phase and heavy phase of the blood to move past the piston.
 4. The assembly of claim 3 wherein the piston is formed of polystyrene having a specific gravity of substantially 1.06.
 5. The assembly of claim 3 wherein said compressible sleeve is made of closed-cell elastomeric sponge material having a smooth surface. 